The preparation of polyesterpolyols for use in making polyester urethanes has been practiced commercially for some 20 years. (See J. H. Saunders & K. C. Frisch, "Polyurethanes: Chemistry and Technology," Part I, Interscience, New York-London (1962) pp. 1-15). Most of the work which has been done in this field has been concerned with utilization of chemical raw materials produced in large volume which are economically attractive and which impart desirable properties to the derived polyurethane compositions. As the basis for most polyesterurethane compositions produced commercially up to the present time, polyesterdiols and polyesterpolyols derived from adipic acid together with various lower aliphatic primary and/or secondary diols and triols have been employed. Epsilon-caprolactone also has found widespread use as the source of polyester backbone for many highperformance systems, and to a lesser extent azelaic acid, ortho-phthalic acid and iso-phthalic acid (together with aliphatic diols and triols) have been employed in certain applications.
The development of polyesterpolyols containing the glutarate moiety for use in the manufacture of polyurethane compositions has received relatively little attention in the past because the potential sources of glutarate (glutaric acid, glutaric anhydride and lower dialkyl glutarates) either were not commercially available in large quantities or were too expensive to be competitive with adipic acid, epsilon-caprolactone, etc. Several references do, however, disclose the preparation of poly(alkylene glutarate)s and their use in the preparation of polyurethane compositions. (See British Pat. Nos. 783,615, 802,245, and 882,603; also, U.S. Pat. No. 3,007,899). In these references the glutarate polyesters are mostly derived from glutaric acid; British Pat. No. 882,603 does describe the preparation of a co-polyester from a mixture of dimethyl succinate, dimethyl glutarate, dimethyl adipate and other raw materials by means of a process (zinc acetate catalyst), which would not yield products of the level of quality of the present invention because the residuum of zinc in the product would catalyze the reaction of isocyanates with the polyesterpolyols.
The ready availability of dimethyl glutarate at competitive prices suggests that hydroxyl terminated polyesters thereof could be used advantageously in the production of polyurethanes but heretofore no satisfactory process has been available for mmaking such esters and no entirely satisfactory products have heretofore been available.
It has been proposed to prepare polyethylene terephthalate fibers by transesterification using stannous formate as the catalyst. The products thus produced, however are not useful in the preparation of polyurethane. It is not known that stannous formate cannot be used for catalyzing the transesterification of dimethyl glutarate but it is obvious from its known properties that it would be the least desirable of the stannous alkanoates. It is not unusual for the lowest member of a series to have atypical properties and this is indeed true with formic acid and its salts. Thus formic acid is known to be an oxidizing and a reducing agent, and conceivably could have an adverse reaction on some of the components of the system. For example, the stannous formate is likely to become contaminated with oxytin compounds through oxidation and such a catalyst, while useful in terephthalate manufacture, would not be suitable for the polyester glutarate manufacture of the invention because the tetravalent tin maintains its activity as a catalyst for catalyzing the reaction of the diisocyanates with active hydrogen compounds, and would therefore interfere with the use of such polyesters in the manufacture of polyurethanes. Moreover, a formate is not, strictly speaking, an alkanoate, or other aliphatic or aromatic carboxylate, as the carboxyl group is not attached to an organic radical.